The present invention is directed to integrated circuits and their processing for the manufacture of semiconductor devices. More particularly, the invention provides a method and system for quality assurance of reticle fabrication for the manufacture of integrated circuits. Merely by way of example, the invention has been applied to a reticle blank. But it would be recognized that the invention has a much broader range of applicability.
Integrated circuits or “ICs” have evolved from a handful of interconnected devices fabricated on a single chip of silicon to millions of devices. Current ICs provide performance and complexity far beyond what was originally imagined. In order to achieve improvements in complexity and circuit density (i.e., the number of devices capable of being packed onto a given chip area), the size of the smallest device feature, also known as the device “geometry”, has become smaller with each generation of ICs. Semiconductor devices are now being fabricated with features less than a quarter of a micron across.
Increasing circuit density has not only improved the complexity and performance of ICs but has also provided lower cost parts to the consumer. An IC fabrication facility can cost hundreds of millions, or even billions, of dollars. Each fabrication facility will have a certain throughput of wafers, and each wafer will have a certain number of ICs on it. Therefore, by making the individual devices of an IC smaller, more devices may be fabricated on each wafer, thus increasing the output of the fabrication facility. Making devices smaller is very challenging, as each process used in IC fabrication has a limit. That is to say, a given process typically only works down to a certain feature size, and then either the process or the device layout needs to be changed. An example of such a limit is chemical dry etching process used for the manufacture of integrated circuits in a cost effective and efficient way.
The manufacturing of integrated circuits involves various processes. For example, the processes include, inter alia, wafer growth, photolithography, doping, oxidation, deposition, etching removal, and epitaxial growth.
Semiconductor devices and circuits are formed in wafers, which serve as substrates. Generally, single-crystal substrates, which are made from a single material with crystals formed by atoms all aligned in a specific direction. The process of waver creation usually involves creating a large ingot of semiconductor materials, aligning the ingot, removing impurities, slicing ingot into thin wafers, and polishing the sliced wafers.
Generally, photolithography process is used to define and shape specific areas of the wafer to suit particular design of integrated circuit. Usually, a layout design is used to create an optical mask (or reticle pattern, depending on application). The wafer surface is usually covered with a layer of photoresist. The wafer is then exposed to light through the optical mask. After light exposure, the areas of photoresist that were exposed to light are removed using chemical process. As a result, the wafer contains both clear areas (where photoresist is removed) and areas blocked by photoresist. Next, various processes (such as etching, oxidation, diffusion, etc.) only affecting clear areas are performed. After various processes are finished, photoresist materials are then removed.
Photolithography process is crucial to the process of semiconductor fabrication. For example, inaccurate reticle patterns lead to low quality and/or unusable end products. Over the past, various conventional techniques have been developed to ensure the accuracy of photolithography processes. Unfortunately, these techniques have been inadequate.
Therefore, it is desired to have an improved system and method for ensuring the quality of reticles used for the manufacturing of integrated circuits.